Dental burs are used to drill into teeth, and to shape internal and external tooth surfaces. But their tooth material is hard, and a hard, sharp bur is needed to do the work. In order to do the work with less trauma to the patient, such burs are operated at very high speeds, and particular care is taken with lubrication and cooling. Still, however careful and advanced are the burs and the skills of the dentist, the patient will be traumatized to some extent. Lessening of this tendency requires attention to a variety of causes. While the improvement to each of these causes may individually be very small, the cumulative effect to the patient may be very important.
To the dentist, the cost of burs is important, and the need to change them during a procedure because they become dull is a decided nuisance. The enhancement of durability then has two aspects. One is that a bur which remains sharp longer can in the long run be less traumatic. Another is that a bur which is likelier to remain optimally sharper for a longer period of time and therefore be less expensive.
As a consquence of this invention, drilling and grinding speeds can be shortened, vibration effects from a non-uniformly worn bur can be reduced, and to these improvements can additionally be added improved lubricity and heat transfer properties. A problem that is inherent in conventional efforts to make a sharp and durable bur is that these materials tend to be brittle, and crack and break. Breakage during usage represents a danger to the patient. A piece of the bur may come loose and not be readily retrievable, or may jam in a tooth crevice, requiring sacrifice of some of the tooth. These tendencies may be countered not only by maintaining sharpness longer, but also by providing toughness as well. With conventional burs, these objectives are counter to one another. This invention enables them to be obtained or at least approached at the same time.
While efforts have been made to accomplish the above objectives, the existing bur generally involve composite structures in which cutting bodies are bonded or embedded in a substrate. An example is tungsten carbide cutting inserts bonded to a stainless steel substrate. Such an arrangement provides multiple opportunities for failure.
Optionally an entire bur might be made of tungsten carbide to resist the tendency of the bur to fragment, but this is relativly expensive, and if used should have a means to extend its useful life.
As another example, diamond coated burs have diamond crystals embedded in a relatively soft substrate. When the substrate erodes, the crystals are lost, and the bur no longer functions. Coating a diamond surface to protect the substrate lengthens the life of the bur. It is an object of this invention to provide a more durable dental bur, which can if desired also have improved inherent lubricity and heat conductivity, all to the econonmic benefit of the dentist, and to the reduction of trauma to the patient.